Balancing the Risks of Mercury

The Mole ... for anyone inspired to dig deeper into chemistry Issue 04 | July 2013 Balancing the risks In this issue Geosmin Why the smell of a wet rugby pitch could be the of mercury key to survival Vitamin C A forthcoming UN treaty aims to cut the amount of mercury used all over the How much world in an attempt to reduce its toxic effects. Does an outright ban go too is in your orange? far? Ian Farrell investigates Repairing © shutterstock teeth Cutting-edge chemistry to restore tooth enamel A good read Science books for the summer Earn while you learn Higher apprenticeships could be your debt-free route to a degree

Editor Karen J Ogilvie Assistant editor David Sait ChemNet content Mercury is a pretty special metal. It’s one of only two the skin or breathed in, which means that chemists and Francesca Burgoyne Production elements in the periodic table to exist as a liquid engineers are always on the lookout for materials that Scott Ollington and Emma Shiells at room temperature, and its slippery, reflective can replace it. Publisher appearance once gave it the historical nickname Scientists have become more aware of the poisonous Bibiana Campos-Seijo ‘quicksilver.’ It’s used in all manner of applications, effects of mercury over time, but historically it was con- The Mole is published six times from producing industrial chemicals and fluorescent sidered to have health benefits. Back in Victorian times, a year by the Royal Society of light bulbs to dental fillings and medical preservatives. Chemistry, Thomas Graham mercury metal was prescribed by doctors as a cure for House, Cambridge, Mercury has also been used for centuries in constipation, among other things. You’d be strongly CB4 0WF. thermometers and barometers. 01223 420066 advised not to swallow or handle it today! email: [email protected] Toxicity The United Nations (UN) has just spent six years working www.rsc.org/TheMole

But there is one big problem with mercury – its toxicity. on a treaty that aims to eliminate or reduce mercury use © The Royal Society of Chemistry, Mercury is harmful when swallowed, absorbed through throughout the world. The agreement, which is due to 2013. ISSN: 2049-2634

www.rsc.org/TheMole Registered Charity Number 207890 slowly. It’s also able to cross the blood–brain barrier very easily. Mercury that exists as the famous liquid metal – as found in thermometers and pressure gauges – is less dangerous. If you swallowed any, it would probably pass through your digestive system without causing you too much trouble, because it’s absorbed very slowly. That said, it can still be dangerous in large quantities or if exposure goes on for a long time. But the liquid metal form of mercury is much more dangerous when its vapours are breathed in. This can cause tremors, gingivitis (bleeding gums) and other neurological problems. It is a big problem in parts of the world where mercury is used in industrial processes, like mining. The risk from fish

© shutterstock © Mercury is found in many rocks and minerals, including coal. Although the concentrations involved are low, the At the top of the food be signed by all 193 UN member countries in October chain, oily fish like 2013, aims to prevent a range of health issues, the amount of coal the world burns in a year is huge, which tuna and swordfish can most common of which relate to the brain. Symptoms of means lots of mercury is released into the environment be relatively high in this way. It comes back down to earth in rain and snow methylmercury severe mercury poisoning include: tremors and shaking; depression and insomnia; and reduced learning and finds its way into rivers, seas and oceans where capabilities, especially in young children. microorganisms like algae and plankton absorb it and convert it to the more toxic methylmercury form. Methylmercury Not all types of mercury are equally poisonous though, Over time, these microorganisms are eaten by small and experts are keen to point out that the risks posed fish that, in turn, are eaten by bigger fish, and the by the metal should be properly evaluated and kept methylmercury accumulates in their flesh. These bigger in perspective. The toxic effects of mercury depend fish are eaten by even bigger fish until we get to the top on its chemical form and the route by which it gets of the food chain, where oily fish like tuna and swordfish into the body in the first place. The most toxic form is can be found to be relatively high in methylmercury. + This can be a problem for families that live almost methylmercury, written as CH3Hg . exclusively on such fish, such as Inuit and populations Methylmercury affects the immune system, alters our from the Seychelles. genetic code and enzyme systems, and damages the nervous system, affecting our sense of touch, smell, The UN and the World Health Organization (WHO) are so The Minamata memorial, taste and sight. It’s particularly damaging to babies worried about this effect that it is mentioned specifically in memory of those in the womb, who are 5–10 times more sensitive in the treaty that is aiming to reduce mercury. They have poisoned by the 1950s than adults, and it usually gets into the body through named the treaty after the Japanese city of Minamata industrial release of – one of the most famous sites of methylmercury methylmercury into ingestion. It’s so dangerous because it’s absorbed more poisoning through fish. Between 1932 and 1968, the bay readily than other forms of mercury and excreted more waste water containing mercury from an industrial plant was dumped in nearby rivers, where it caused horrific neurological problems in the local fish-eating population. The symptoms – which can vary from tremors and shakes to physical abnormalities – are known as Minamata disease. Although the link between burning coal and methylmercury in fish is well established, the risks posed are not on the same scale as the Minamata disaster. While populations who eat significant amounts of fish are thought to be at risk from methylmercury poisoning, there are also arguments that the health benefits of their oily-fish diet actually outweigh the problems from the mercury. The human body has defence mechanisms in place against mercury, reacting it with another metal – selenium – to produce mercury selenide (HgSe). This is a my sutton-hibbert/Al jeremy ©

totally insoluble in water, and therefore not ‘biologically a rrell/mrc available’ to the body. It’s a neat trick, but to do it we need some selenium in our diet. And one of the best sources of selenium is (conveniently) also oily fish. This may be why scientists have found bigger methylmercury health problems in populations that eat fish that are low in selenium (such as shark or pilot whale) than those who eat selenium-rich species (like tuna and swordfish). Gold rush Breathing in mercury fumes is far more dangerous than eating it, and this is worse when mercury is hot. For a metal, mercury has an extremely low boiling point, just 388˚C. This means that, as it gets warmer, the amount of mercury gas increases – just like water vapour appearing over heated water. In this situation, it’s all too easy to breathe in way more mercury than your body saving light bulbs may be a source of mercury pollution Thiomersal (a compound can cope with. if they are dumped in landfill sites, but using them in the of mercury) is added first place means burning less coal in power stations. to vaccines as a Although exposure to mercury vapour is usually a Careful balances must be made. preservative, to prevent result of industrial accidents, workers at gold mines the growth of fungi and in developing countries are often exposed to such Some uses of mercury in the developing world are bacteria hazards as part of their normal everyday job. They use actually beneficial to health. Thiomersal (sodium liquid mercury to dissolve gold from finely powdered ethylmercurithiosalicylate) is added to vaccines as rock, forming a gold–mercury amalgam. The mercury is a preservative, to prevent the growth of fungi and then boiled off to leave behind the gold. This process bacteria. Without it, many countries would struggle to is extremely dangerous: young children and new born maintain vaccination programmes that save millions of babies are particularly susceptible to brain damage, and lives. Using mercury in this way is considered safe by exposure levels are so large that they overwhelm the the WHO, and is specifically excluded from the treaty. body’s nature defence mechanisms. The need to consider factors such as these when The consequences of change making decisions about the future use of mercury is Mining gold with mercury is just one of the activities perhaps why it has taken six years for the UN to draft that the UN’s Minamata treaty hopes to eliminate, but the Minamata treaty. There are bound to be those that all such changes have huge social impacts on the way think the legislation goes too far, as well as experts Find out that many people live and these must also be taken into who say it doesn’t go far enough. The secret is balance, account. In the case of mining, an instant ban would and compromise. more seriously affect the way that millions of miners all over The UN’s treaty is a brave and significant move, but its Learn more about the the world work and support their families, so a gradual effects of mercury in the effects won’t be seen for a long while. It will take time to phase-out of the practice may be better. environment with the US phase out the industrial processes that spread mercury Geological Survey: Similarly, turning away from coal as a source of energy around the planet, and even then there is enough of the http://on.doi.gov/19LjxsI could help to reduce the amount of mercury that metal already in the biosphere for its effects to be seen ends up in the environment, but doing so could harm for decades to come. However, the Minamata treaty is the economic and social development of many poor a step in the right direction and a recognition of the countries, and the people that live in them. Energy- trouble that this remarkable metal can cause.

Mercury and vaccines In the west, we produce vaccines in single-use sealed which can cause all manner of health problems, and vials that are prepared under strictly sterile conditions, even death. but this is not the case everywhere in the world. In To prevent this, thiomersal is added to bottles. Its developing countries it’s cheaper for a nurse to inject antimicrobial properties prevent the bacteria and fungi many people from a larger, multi-dose bottle of vaccine. multiplying and ensure the vaccine is safe to inject. These larger bottles take up less space in cold storage Without mercury, such vaccination programmes would and refrigerated transport, making them more practical have to use more expensive single-use vaccine doses, and less expensive on a per-dose basis. The only meaning fewer people could be treated. For this reason problem is that, once they are opened, the bottles are mercury-containing vaccines solve more problems than susceptible to contamination by bacteria and fungi, they cause and are not banned under the UN treaty.